Washing machine tank provided wtih external reinforcing cap on bottom wall

ABSTRACT

The present invention relates to a washing machine tank ( 1 ), of the type provided with a basically cylindrical structure obtained by moulding plastic materials, designed to house a rotary metal drum, characterised in that it is provided with a smooth bottom wall ( 2 ) with central hole, against which a circular cap ( 3 ) is exactly engaged and permanently fixed with concavity facing the bottom wall, with a cylindrical nozzle in central position designed to be perfectly aligned with the central hole of the bottom wall.

The present patent application for industrial invention relates to awashing machine tank provided with an external reinforcing cap on thebottom wall.

As it is known, the washing unit of washing machines or dryer/washercombos comprises a basically cylindrical drum designed to be loaded withlaundry, which rotates inside a tank obtained by moulding plasticmaterials.

A similar tank is frontally provided with a large opening to load thelaundry, while the bottom wall is provided with a central hole that endsin a rear cylindrical nozzle, where the shaft protruding from the bottomwall of the drum contained in the tank is exactly inserted, with theinterposition of a bearing support.

In particular, the shaft slightly protrudes outside the tank in order tobe coupled with the electrical motor designed to drive the drum intorotation.

In some cases, the electrical motor is mounted in peripheral positionwith respect to the bottom wall of the cylindrical tank; in such a case,a drive belt is provided to ensure the joint rotation of the shaft ofthe electrical motor and the shaft of the drum, which are both suitablyprovided with corresponding pulleys.

In other cases, the so-called “direct drive” technology is used,according to which the stator of the electrical motor is mounted in thecentre of the bottom wall of the tank in such a way that the rotor isdirectly splined to the shaft of the drum.

In both cases, however, the bottom wall of the washing machine tank mustbe characterised by high structural rigidity in order to withstandwithout damages the high mechanical stress induced by the centrifugalforce generated by the mass of the laundry contained in the rotatingdrum.

So far, the said rigidity of the bottom wall has been guaranteed bymeans of a network of stiffening ribs provided on the outside of thetank.

When the presence of the said ribs is not sufficient, the bottom wall ofthe tank is given an “omega” profile in which some sections of the wallprotrude inwards.

In fact, such a configuration gives the bottom wall of the tank a highinertia momentum.

A careful examination of the state of the art has identified severalcritical aspects.

In particular, the formation of the external stiffening ribs requires alarge use of moulding material and sophisticated expensive moulds, withvery long moulding time especially due to the need to cool down theribs.

By considering that the market offers different models of washingmachines in terms of rotation speed of the drums (from 400 to 1,600rpm.), it is clear that each model of washing machine must be providedwith a tank with specific mechanical resistance characteristicsaccording to the different stress imposed by the rotation of the drum.

In view of this, a manufacturer of washing machine tanks must produce atleast five different models of tanks, each of them with differentrigidity and resistance according to the rotation speed of the specificappliance.

Moreover, the tanks with bottom wall provided with “omega” profile areimpaired by the fact that they create considerable turbulence in thewater mass contained inside the tank, with consequent high noise levelinside the appliance, formation of foam that requires more rinsingwater, and considerable washing residues in the concave areas of thebottom wall that are not removed by the rinsing water.

The washing residues originate the so-called “biofilm”, which isconsidered detrimental because it favours the proliferation of bacteriaand consequent production of bad odours.

The purpose of the present invention is to find a solution to theaforementioned problems of the prior technique, in order to reduceproduction costs and increase technical-functional efficiency andversatility considerably.

The inventive idea of the present invention consists in a specialcomposite structure of the bottom wall of a washing machine tank.

More precisely, the tank of the invention is provided with a bottom wallwith smooth surface both internally and externally.

This allows to eliminate the traditional stiffening ribs that protrudeoutwards and the raised areas with that protrude inwards, of the typeused in the bottom wall of tanks provided with “omega” profile.

In this case the task to give the necessary rigidity and resistance tomechanical stress is entrusted to a circular cap designed to be exactlyfitted against the external side of the bottom wall of the tank.

The plastic moulded cap is preferably provided with a plurality ofspokes, being otherwise defined as cross-piece.

Considering that the spokes of the cap are internally hollow, it appearsevident that, in cooperation with the external side of the flat bottomof the tank of the invention, the spokes originate a box-shapedstructure with multiple spokes, which is effectively able to guarantee aconsiderable inertia momentum both with respect to flexural andtorsional stress.

If considered individually, both the smooth bottom wall of the tank andthe cap have modest inertia values due to reduced thickness.

Their stable coupling, however, allows to create the box-shapedstructure effectively provided with mechanical characteristicscompatible with the correct operation of a washing machine.

The advantages of the invention appear evident from this firstdescription.

First of all, the presence of a perfectly smooth bottom wall ensuresbetter practical and economic characteristics with reference tomoulding, not only because of the lower complexity of the moulds, butalso because of the lower quantity of plastic material used.

The elimination of the inward protruding sections that are typical oftanks with “omega” bottom completely prevents the formation of theundesirable biofilm.

The presence of the smooth bottom wall of the tank of the inventiongenerates an excellent distribution of the surface tension that tend tobe created in a totally non-uniform way in the more complicatedstructures of the pre-existing tanks, impairing the mechanicalcharacteristics of the same tanks.

Moreover, the composite structure of the bottom wall of the tank of theinvention ensures practical and economic characteristics also withreference to the production of different models of tanks for washingmachines with different rotation speeds.

As mentioned earlier, according to the prior technique, each specifictype of washing machine requires a specific tank with specific rigidityand mechanical resistance properties according to the maximum rotationspeed.

Because of the present invention, all different types of washingmachines use the same type of tanks, being provided that the task toguarantee the correct index of mechanical resistance to the bottom wallof the tank is entrusted to the cap with multiple spokes.

In view of the above, a manufacturer that makes use of the technology ofthe invention will produce a single model of tank, which will be adaptedto each specific model of washing machine by means of a diversifiedproduction of caps (according to the different thickness and profile ofthe caps).

The need to produce a different range of caps is certainly morepractical and cost-effective compared to the current need to produce adifferent range of tanks.

Finally, it must be noted that the favourable weight/performance ratiodetermined in the tank of the invention because of the assembly betweenthe bottom wall of the tank and the cap contributes to optimise thetraditional appendixes provided on the perimeter of washing machinetanks.

Reference is made to the appendixes designed to favour the assembly inperipheral position of the electrical motor designed to drive theinternal drum into rotation, and also to the appendixes used to applyfixing means used to join the tank to the bearing case of the householdappliance during packaging and transport operations (when the tank,which is usually mounted on elastic elements; is subjected to undesireddangerous shocks).

For clarity purposes the description of the invention continues withreference to the enclosed drawings, which only have an illustrative, notlimiting purpose, whereby:

FIG. 1 is an axonometric view of the tank of the invention, without thereinforcing cap;

FIG. 2 is an axonometric external view of the said cap;

FIG. 3 is an axonometric internal view of the said cap;

FIG. 4 is an axonometric view of the aforementioned components one infront of the other one, without permanent fixing;

FIG. 5 is an axonometric view of the tank in assembled condition;

FIG. 6 is an axonometric exploded view of the tank, in the embodimentdesigned to be associated with the corresponding electrical motoraccording to the direct drive technology.

With reference to FIG. 1, the tank of the invention (1) is usuallycomposed of a plastic moulded cylindrical structure and designed to befrontally closed with a circular flange (not shown in the enclosedfigures) provided with a large opening used to load laundry inside thetraditional rotary drum (not shown in the enclosed figures) housed inthe tank.

As mentioned earlier, the peculiarity of the new tank (1) consists inthe presence of a smooth bottom wall (2) without stiffening ribs orinward projecting areas.

The wall (2) is provided with a central hole (2 a) that receives theshaft of the drum housed in the tank (1).

With reference to FIGS. 2 and 3, the second component of the tank (1)consists in a sort of circular cap (3) provided with a plurality ofinternally hollow spokes (3 a) obtained by moulding plastic materials.

In particular, the spokes (3 a) protrude from a central cylindricalnozzle (3 b) and are joined at the peripheral ends with the internallyhollow annular border (3 c) of the cap (3).

As shown in FIGS. 2 and 3, the central nozzle (3 b) is considerablylonger than the thickness of the annular perimeter border (3 c); becauseof this, the spokes (3 a) have a section with decreasing height from thecentre to the peripheral area.

The cylindrical nozzle (3 b) is designed to house a metal bearingsupport (SP) that receives exactly the shaft of the drum after passingthrough the hole (2 a) of the bottom wall (2) of the tank (1); referenceis made to FIG. 2 that shows the said support (SP) in an exploded view.

The bearing support (SP) is preferably co-moulded with the cap (3).

In any case, the cap (3) is designed to be fixed in external position onthe flat bottom wall (2) of the tank (1), with the concave side facingthe flat wall (2).

In order to guarantee the mutual coupling between the two components,the cap (3) has a basically identical diameter as the bottom wall (2) ofthe tank (1) and the central nozzle (3 b) of the cap (3) is perfectlyaligned with the hole (2 a) obtained in the bottom wall (2).

The cooperation between the cap (3) and the bottom wall (2) of the tank(1) allows to obtain a box-shaped structure on the back of the tank,which is composed of a series of radial compartments (V1), each of themis bordered by one of the spokes (3 a) of the cap (3), and an annularcompartment (V2) bordered by the annular border (3 c) of the cap (3).

The presence of the box-shaped structure allows the bottom wall (2) toacquire the necessary resistance to withstand without damages themechanical stress transmitted by the rotations of the shaft of the drumfull with wet laundry.

The stable fixing of the cap (3) against the bottom wall (2) of the tank(1) can be obtained according to different suitable modes, such asgluing, welding or screwing.

The cap (3) can be also provided on the external side with basicallycylindrical appendixes (4, 5) obtained during the same process and withthe same moulding material used for the cap (3).

The appendixes (4, 5) have a parallel position to the central nozzle (3b) and are designed to favour the application of the means used toensure the stable fixing of the entire tank (1) to the bearing structureof the washing machine during packaging and transportation.

To that end, each appendix (4, 5) is frontally provided with acorresponding axial hole (4 a, 5 a) used to screw a corresponding screw.

In particular, in the embodiment of the cap (3) shown in the enclosedfigures, a first opposite pair (4) of appendixes is provided at a higherheight directly protruding from the annular border (3 c), and a secondpair (5) of appendixes is provided at a lower height protruding on thefront of corresponding small hollow arms (5 b) that protrude radiallyfrom the annular border (3 c).

Finally, a third pair (6) of similar appendixes is provided between thetwo appendixes of the second pair (6), protruding on the front ofcorresponding small hollow arms (6 b), designed to be used to fix theelectrical motor that drives into rotation the shaft of the drum housedinside the cylindrical nozzle (3 b) of the cap (3) by means of a drivebelt.

Also the appendixes (6) of the third pair are frontally provided withaxial holes (6 a) for suitable fixing screws.

The small radial arms (5 a, 6 a) are provided with correspondinginternal cavities designed to be exactly covered, when the cap (3) isengaged to the bottom wall (2) of the tank (1), by corresponding ears(50 a, 60 a) that protrude from the border of the bottom wall (2) of thetank (1) to generate relevant box-shaped structures.

In this way, also the small arms (5 a, 6 a) are advantageously givenhigh mechanical resistance during operation.

Finally, FIG. 6 shows the embodiment of the cap (3) designed to mountthe electrical motor according to the direct drive technology.

In such a case, the external surface of the cap (3) is provided withthree fixing holes (3 d) for the stator (ST), with a corresponding rotor(RT) that rotates outside it splined to the shaft of the drum thatpartially protrudes from the cylindrical nozzle (3 b) of the cap (3).

1. Washing machine tank comprising: a basically cylindrical structure(1) obtained by moulding plastic materials, designed to house a rotarymetal drum, said cylindrical structure (1) being provided with a smoothbottom wall (2) with a central hole (2 a) and a cap (3) exactly engagedand permanently fixed to said bottom wall (2) of the cylindricalstructure (1), said cap (3) having a cylindrical nozzle (3 b) in centralposition designed to be perfectly aligned with the central hole (2 a) ofthe bottom wall (2), wherein said cap (3) is obtained by mouldingplastic materials, said cap (3) being fixed in external position,against to said bottom wall (2) of the cylindrical structure (1) bymeans of gluing, welding or screwing, said cap (3) having a concave sidefacing the smooth bottom wall (2) of said cylindrical structure (1). 2.Washing machine tank as claimed in claim 1, wherein the nozzle (3 b) ofthe cap (3) houses a metal bearing support (SP).
 3. Washing machine tankas claimed in claim 1 wherein the cap (3) is provided with a series ofspokes (3 a) starting from the central nozzle (3 b) with correspondingcavities facing the bottom wall (2) of the tank (1).
 4. Washing machinetank as claimed in claim 3, wherein the spokes (3 a) of the cap (3) arecoupled at the ends with an annular border (3 c) with cavity facing thebottom wall (2) of the cylindrical structure (1).
 5. Washing machinetank as claimed on claim 4, characterised in that the central nozzle (3b) of the cap (3) is longer than the height of the annular border (3 c)and, consequently, the spokes (3 a) have a decreasing height from thecentre to the peripheral area.
 6. Washing machine tank as claimed inclaim 4, wherein the annular border (3 c) of the cap (3) is providedwith appendixes (4, 5, 6) used to mount the fixing means to the bearingstructure of the washing machine and the electrical motor.
 7. Washingmachine tank as claimed in claim 5, wherein the appendixes (4, 5, 6)have a basically cylindrical structure parallel to the central nozzle (3b) of the cap (3) and are provided with relevant axial holes (4 a, 5 a,6 a) used to insert screws or similar fixing means.
 8. Washing machinetank as claimed in one or more of the claim 4, wherein a first oppositepair (4) of appendixes designed to receive the fixing means of thebearing structure of the washing machine protrudes directly from theannular border (3 c) of the cap (3) and a second opposite pair (5) ofappendixes protrudes at a lower height protruding on the front ofcorresponding small arms (5 b) that protrude radially from the annularborder (3 c).
 9. Washing machine tank as claimed in claim 5, wherein theappendixes (6) designed to favour the mounting of an electrical motorprotrude from corresponding small arms (6 b) that protrude radially fromthe annular border (3 c) of the cap (3).
 10. Washing machine tank asclaimed in claim 1, wherein the small radial arms (5 a, 6 a) (5 b, 6 b)protruding from the cap (3) are provided with internal cavities facingthe bottom wall (2) of the cylindrical structure (1) of the tankdesigned to engage exactly against corresponding ears (50 a, 60 a)protruding from the border of the bottom wall (2).
 11. Washing machinetank as claimed in claim 1, wherein the cap (3) is frontally providedwith holes (3 d) for direct mounting of a stator (ST) of an electricalmotor, with rotor (RT) splined to the shaft of the drum that protrudesslightly from the nozzle (3 b).